I'm using a the WPF DataGrid from the wpf toolkit and a TimePicker from AvalonControlsLibrary to insert a collection of TimeSpans. My problem is that bindings are not working inside the DataGrid, and I have no clue of why this isn't working.

Here is my setup:

I have the following XAML:

<Window x:Class="Views.TestMainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:wpf="http://schemas.microsoft.com/wpf/2008/toolkit" xmlns:a="http://schemas.AvalonControls/AvalonControlsLibrary/Controls" SizeToContent="WidthAndHeight" MinHeight="250" MinWidth="300">
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="*" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>
    <GroupBox Grid.Row="0">
        <GroupBox.Header>
            Testing it:
        </GroupBox.Header>
        <wpf:DataGrid ItemsSource="{Binding Path=TestSpans}" AutoGenerateColumns="False">
            <wpf:DataGrid.Columns>
                <wpf:DataGridTemplateColumn Header="Start">
                    <wpf:DataGridTemplateColumn.CellEditingTemplate>
                        <DataTemplate>
                            <a:TimePicker SelectedTime="{Binding Path=., Mode=TwoWay}" />
                        </DataTemplate>
                    </wpf:DataGridTemplateColumn.CellEditingTemplate>
                    <wpf:DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding}" />
                        </DataTemplate>
                    </wpf:DataGridTemplateColumn.CellTemplate>
                </wpf:DataGridTemplateColumn>
            </wpf:DataGrid.Columns>
        </wpf:DataGrid>
    </GroupBox>
    <StackPanel Orientation="Horizontal" HorizontalAlignment="Right" Grid.Row="1">
        <a:TimePicker SelectedTime="{Binding Path=SelectedTime, Mode=TwoWay}" />
    </StackPanel>
</Grid>

And this is my ViewModel:

Imports System.Collections.ObjectModel

Namespace ViewModels

Public Class TestMainWindowViewModel

    Private _selectedTime As TimeSpan = DateTime.Now.TimeOfDay
    Public Property SelectedTime() As TimeSpan
        Get
            Return _selectedTime
        End Get
        Set(ByVal value As TimeSpan)
            _selectedTime = value
        End Set
    End Property

    Private _testSpans As ObservableCollection(Of TimeSpan) = New ObservableCollection(Of TimeSpan)
    Public Property TestSpans() As ObservableCollection(Of TimeSpan)
        Get
            Return _testSpans
        End Get
        Set(ByVal value As ObservableCollection(Of TimeSpan))
            _testSpans = value
        End Set
    End Property

    Public Sub New()
        _testSpans.Add(DateTime.Now.TimeOfDay)
        _testSpans.Add(DateTime.Now.TimeOfDay)
        _testSpans.Add(DateTime.Now.TimeOfDay)
    End Sub

End Class

End Namespace

I'm starting this window in application.xaml.vb like this:

Class Application

    ' Application-level events, such as Startup, Exit, and DispatcherUnhandledException
    ' can be handled in this file.
    Protected Overrides Sub OnStartup(ByVal e As System.Windows.StartupEventArgs)
        MyBase.OnStartup(e)
        Dim window As Views.TestMainWindow = New Views.TestMainWindow

        window.DataContext = New TestMainWindowViewModel()

        window.Show()

    End Sub

End Class